1. Field of the Invention
The present invention relates generally to the art of digital scanning, and more particularly, to an apparatus for digitally archiving analog images from film negatives and positives which are projected onto the scanner by transillumination of the film.
2. Discussion of the Prior Art
The extent of the World's knowledge as expressed in drawings and text is significant. The problems of storing, maintaining and then finding documentation in a timely fashion have been addressed, but even near-perfection in archiving techniques is yet to be obtained. Drawings which were created by hand in the last century have been ravaged by discoloration, wear, dirt, smudging, tearing and taping, and many have been folded, carelessly used, or stored in a debilitating environment.
Further, an amazing percentage of "originals" are not true originals. Second or third generation copies have become de facto originals, with each succeeding copy representing a poorer rendition of its parent. Many of these pseudo-originals are diazo sepias on paper or mylar, and as diazo dyes are transient and impermanent, the images fade and the changes made to those drawings, usually in pencil, are so different than the sepia images themselves that the combination is difficult or impossible to copy again, even when using the images for contact prints.
It was because of the foregoing problems with traditional archiving techniques that camera/projectors were introduced in the industry. Such camera/projectors utilize film sizes of 105 mm (Nominal 4.times.6 inches), 8.5.times.11 inches with a 7.25.times.9.5 inch image, or a nominal 11.times.17 inch size, to preserve the original image.
Particular devices which brought the industry some startling restorative effects are described in a long list of patents awarded this same inventor, of which U.S. Pat. Nos. 3,639,054 and 3,762,816 are typical. These devices combine front and back lighting of an original with superior flat field lenses, and employ hybrid chemistry in a combination with selected film emulsions to retain lines beyond the range of recovery of conventional scanning devices, even when manual intervention techniques are employed.
More importantly, conventional filming methods achieve restoration automatically, without human intervention or editing, and in seconds instead of hours. These known methods drop out discoloration and many of the artifacts, such as tape, introduced into the original drawing by aging and misuse, and they reduce a wide variance of line intensity to a common black and white denominator.
The same problems inherent in archiving original drawings prevent computer technology from bearing on the problems of warehousing and finding pertinent documentation. Digital paper scanning seemed an obvious approach and has been quite successful with small originals and originals having good images. However, most engineering drawings are not small and many have images whose quality ranges from indifferent to impossible.
Further, conventional paper scanners for large drawings have several limitations. They almost invariably have optical systems which use multiple side-by-side objective lenses, with each capturing only a part of the total image as the scanner passes over the original. Such tandem optics present an alignment problem, and distortion is inevitable.
In addition, digital paper scanners which address the originals themselves require multiple test passes, intuitive manual thresholding and close attention of the operator for minutes or hours. In bad cases, restoration can never be achieved comparably to the results which can be obtained in a camera designed for archiving the original in an analog format on film, and the camera does the job in seconds.
During the last decade it has been possible to achieve image enhancement photographically by making film negative miniatures (not microfilm) and then projecting back to full size on photo sensitive media with point source light to capture all the sharp detail found in the negative in a form which could be utilized by a conventional paper scanner. This conventional method provides many advantages over scanning the original drawing directly. For example, when a drawing is reduced onto miniaturized film, the rapid aging inherent with paper copies is arrested by the archival film at the same time that the film enhances the stored analog image. In addition, the film represents a permanent analog image that may be archived for later reference, even if it is not scanned immediately.
In contrast to the use of this known method, if the original drawing was digitized directly, the data would represent the analog image at the time of the scan, but the original would continue to deteriorate. Thus, the original would not be preserved for use if it was later necessary to scan the analog image, e.g. upon the development of improved digital scanning technology.
Another advantage of archiving drawings on film resides in the enhancement provided by the photographic process. For example, by suppressing artifacts and debris that have collected on the original drawing, film images have less information to be detected during scanning. Thus, compression of the digital data obtained from a scan of a blow-back print of the film image is easier to achieve and requires less storage than would be required otherwise. A drawing which requires 2 megabytes of storage in a conventional paper scanner may easily be retained and improved in 300 kilobytes of storage when the image is first transferred to film and then blown back to original size before being scanned.
Digital film scanners are available which provide advantages over paper scanners primarily as a result of the enhancements obtained in making the analog film image from the original drawing, as discussed above. For example, by transferring the image to film prior to scanning, the need for functions such as spatial filtering, edge sharpening, edge smoothing, contrast enhancement, thresholding, adaptive software thresholding, warping/rubber sheeting, frequency domain analysis and others is frequently obviated.
However, drawbacks to conventional film scanners do exist. For example, when drawings are reduced to extremely small film sizes, such as 35 mm aperture cards or the like, the image deteriorates due to the degree of reduction and is not capable of being returned to actual size without suffering in quality. Thus, even if the film image is scanned and enlarged through the use of software, the resolution of the image is poor.
Generally, the quality in a reduced image is directly related to the degree of reduction used; the more modest the reduction, the better the quality. This axiom does not apply where the degree of reduction is between 0 and about 4.times. smaller than the original, where the quality remains the same without adverse effect. Examples of conventional film sizes used in archiving drawings include 35 mm, which requires reductions of up to 36.times. the original size; 105 mm, which requires reductions up to 10.times. or 11.times.; 8.5.times.11 inches, which requires reductions of up to 10.times.; and 10 inch roll film, which requires reductions up to only 4.times. to 5.times..
An example of a flow camera for producing film images on 10 inch roll film at a limited reduction factor of about 4.times. to 5.times. illustrated in U.S. application Ser. No. 08/125,444, filed Mar. 2, 1993, which is incorporated herein by this reference. This flow camera is particularly suitable for use in producing film images for conversion into digital format because, as mentioned, no degradation in image quality occurs at reductions of up to about 4.times.. Thus, all of the enhancements obtained through the use of photographic archiving are realized without any of the adverse effects experienced when making reductions of greater than about 4.times..
Conventional film scanners render a resolution that is adjustable up to a defined maximum, e.g. 1200 to 2400 dots per inch (dpi), wherein the maximum value is dependent upon the scanner used and the amount of magnification or reduction of the film image projected onto the scanner. Once the resolution is selected, and the digital data representative of the image is stored, magnification of the image data is restricted by the number of dpi at which the image is captured. For example, an image captured at 1200 dpi that is enlarged by a factor of 4 will have a resolution of 300 dpi. If the image is enlarged by a factor of 10, the resolution of the enlargement will be only 120 dpi.
If a scanner is designed for use with 105 mm film bearing images reduced 10.times. relative to the original drawings, it may be constructed to scan the film using a resolution that will deliver the necessary clarity at the original size of the drawing. However, this same device may not provide enough resolution to permit proper enlargement of an image reduced by substantially more than 10.times. on the film, and will retain more data than is necessary to permit enlargement of an image reduced less than 10.times. on the film. Because the amount of reduction typically varies depending upon the size of the original drawing and the film size onto which it is being transferred, a conventional device designed for use with any one size of film will not provide consistent resolution "at the original" when used with other film sizes.